Image sensing apparatus, control method for illumination device, flash photographing method, and computer program product

ABSTRACT

It is an object of this invention to provide an apparatus which can properly expose a main object regardless of the background conditions. In order to achieve this object, there is provided an apparatus comprising a photometric unit for receiving object light and converting the object light into luminance signals of a plurality of areas, and a control unit for calculating the histogram of the luminance distribution on the basis of the luminance signals of the plurality of areas converted by the photometric unit, and controlling the operation of an illumination device for illuminating the object on the basis of the calculation result.

FIELD OF THE INVENTION

[0001] The present invention relates to illumination control of aphotographing object and flash photographing control.

BACKGROUND OF THE INVENTION

[0002] In conventional image sensing apparatuses, to obtain properexposures, many brightness adjusting techniques of emitting auxiliarylight to an object in advance and controlling, for example, the amountof auxiliary light emitted or the emission time have been proposed.

[0003] A typical brightness adjusting technique in a conventional imagesensing apparatus will be described with reference to FIG. 2.

[0004] Referring to FIG. 2, reference numerals 150 and 152 denoteimaging optical systems for forming an object image on an imaging plane.

[0005] Reference numeral 151 denotes a stop interposed between theimaging optical systems 150 and 152. This stop is generally disposed inan afocal (parallel light) range.

[0006] Reference numeral 161 denotes a photoelectric conversion elementfor converting the amount of light imaged into a quantity of electricityor charge. As this element, for example, an image sensing element suchas a CCD (Charge-Coupled Device) is used.

[0007] Reference numeral 162 denotes a camera signal processing circuitfor converting a sensed signal into, for example, a standard videosignal on the basis of the quantity of electricity obtained from thephotoelectric conversion element 161.

[0008] Reference numeral 13 denotes a recording device for recording thevideo signal having undergone signal processing in the camera signalprocessing circuit 162 as a photographing signal.

[0009] Reference numeral 1 denotes a detection means for generating adetection signal used for exposure control by performing detectionprocessing such as integral processing for the luminance component ofthe video signal having undergone the signal processing in the camerasignal processing circuit 162.

[0010] Reference numeral 2 denotes a predetermined reference valueserving as a reference for exposure control, which is a voltage orcharge generating means.

[0011] Reference numeral 3 denotes a comparing means for comparing thedetection signal with the reference value 2 and outputting a signalcorresponding to the comparison result.

[0012] Reference numeral 4 denotes a flash control means for controllingthe amount of light emitted on the basis of the comparison resultobtained by the comparing means 3.

[0013] Reference numeral 5 denotes a flash unit 5 for emitting auxiliarylight; and 6, an object.

[0014] The operation of the above prior art will be described next withreference to the flow chart of FIG. 3.

[0015] The steps in this flow chart will be sequentially describedbelow.

[0016] Step S1: This step is the beginning of the flow, which starts insynchronism with, for example, the operation of an imaging start switch.

[0017] Step S2: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0018] Step S3: Preliminary emission is performed in a predeterminedlight amount by using the flash unit 5.

[0019] Step S4: At the same time the flash unit 5 emits light, a sensedimage is converted into a captured image signal.

[0020] Step S5: The detection means 1 is used to generate a detectionsignal used for exposure control from the sensed signal.

[0021] Step S6: The flash control means 4 determines an exposure levelfrom the detection signal. If the exposure is proper, the flow advancesto step S6. If an underexposure is determined, the flow advances to stepS7. If an overexposure is determined, the flow advances to step S8.

[0022] Step S7: Preparation for emission is done in the same lightamount as that in the preceding emission, and the flow advances to stepS10.

[0023] Step S8: Preparation for emission is done by increasing theamount of light emitted in accordance with the preceding underexposure.The flow then advances to step S10.

[0024] Step S9: Preparation for emission is done by decreasing theamount of light emitted in accordance with the preceding overexposure.The flow then advances to step S10.

[0025] Step S10: It is checked whether the flash unit 5 is completelycharted. If the flash unit 5 is not completely charged, the flow waitsuntil changing is completed.

[0026] Step S11: At the same time the flash unit 5 emits light, a sensedimage is converted into an image signal by the camera signal processingcircuit 162, and the signal is recorded on the recording device 13.

[0027] Step S12: This flow is terminated.

[0028] With the above operations, proper exposure can be performed inphotographing operation with emission of auxiliary light.

[0029] As described above, preliminary emission of the flash unit isperformed in a predetermined light amount, and main emission isdetermined by the flash control means 4 on the basis of the leveldifference between the detection signal obtained in the preliminaryemission and the reference value 2.

[0030] According to the arrangement of the conventional image sensingapparatus, however, exposure control is performed with reference to thedetection output obtained upon preliminary emission of auxiliary light.According to this exposure adjustment, although it depends on the schemeused by the detection means and its characteristics, in the case ofaverage light measurement which is a general detection technique usingan integrator for averaging the overall brightness of a frame, if a mainobject occupies a high proportion of an imaging range, a proper exposurestate can be obtained. In contrast to this, if the main object occupiesa low proportion of the imaging range, or the background is located faraway from the object or blackish, the above integral detection output isgreatly influenced by the background, and a proper exposure state maynot be obtained for the object.

[0031] Consider the object condition shown in FIG. 4. Referring to FIG.4, reference numeral 6 denotes a main object to be photographed by aphotographer; 21, a tree in the distant background; and 22, thephotographing direction of the photographer. Assume that the object isin an illumination condition that requires auxiliary light.

[0032]FIGS. 5b to 5 d show the images sensed by the image sensingapparatus in the object condition shown in FIG. 4.

[0033]FIGS. 5a and 5 b show the sensed image of the object 6 as a singleperson, whereas FIGS. 5c and 5 d indicate the sensed image of the object6 including two persons exhibiting nearly equal reflectances and locatedat the same distance from the image sensing apparatus.

[0034]FIGS. 5b and 5 d schematically show the degrees of illumination onthe objects at the time of emission of the flash unit in brightness. Asan object is located closer to the photographer (the image sensingapparatus including the flash unit), the object becomes brighter;reflected light from the tree 6 in the background or an object in themore distance background becomes very dark.

[0035] Consider an exposure level based on a comparison between theimages shown in FIGS. 5b and 5 d. Assuming that integral detection isperformed by the detection means in the prior art described above, thedetection output in FIG. 5b is smaller than that in FIG. 5d. This isbecause the main object in FIG. 5d at the short distance occupies ahigher proportion of a detection area 25.

[0036] In controlling the main emission amount with reference topreliminary emission, therefore, although the object distances in FIGS.5b and 5 d are the same, since the detection output at the time ofpreliminary emission of auxiliary light in FIG. 5b becomes smaller thanthat in FIG. 5d, the emission amounts obtained from the above results atthe time of main emission have the relationship represented by “amountin FIG. 5b>amount in FIG. 5d”.

[0037] As described above, if a detection scheme like the above integraldetection scheme is used, control is performed to set the sum total ofluminance signals in the detection area 25 to a predetermined level. If,therefore, an object occupies a low proportion of the overall angle ofview as shown in FIGS. 5a and 5 b, and the background occupies a highproportion, since the output from the detection means based on integraldetection becomes small, the flash control means 4 determines anunderexposure and controls the amount of auxiliary light emitted. As aconsequence, proper brightness control is not performed on the object,and an overexposure occurs.

[0038] In general, such a phenomenon is influenced by the position of anobject, the brightness of a background, the proportion occupied by theobject, and the like.

[0039] Note that the detection area 25 is a frame indicating the entireimaging area (detection area).

SUMMARY OF THE INVENTION

[0040] The present invention has therefore been made in consideration ofthe above problems, and has an object to properly illuminate or flashphotograph a main object regardless of background conditions.

[0041] In order to solve the above problems and achieve the aboveobject, an apparatus of the present invention, according to its firstaspect, is characterized by having the following arrangement.

[0042] The apparatus comprises:

[0043] (A) a photometric unit for receiving object light and convertingthe object light into luminance signals of a plurality of areas; and

[0044] (B) a control unit for calculating a histogram of a luminancedistribution on the basis of the luminance signals of the plurality ofareas converted by the photometric unit, the control unit controllingoperation of an illumination device for illuminating an object based ona result of the calculating.

[0045] An apparatus of the present invention, according to its secondaspect, is characterized by having the following arrangement.

[0046] The apparatus comprises

[0047] (A) a photometric unit for receiving object light and convertingthe object light into luminance signals of a plurality of areas; and

[0048] (B) a control unit for calculating a histogram of a luminancedistribution on the basis of the luminance signals of the plurality ofareas converted by the photometric unit, the control unit controllingflash photographing operation based on a result of the calculating.

[0049] An illumination device control method according to the presentinvention is characterized being configured as follows.

[0050] The illumination device control method comprises:

[0051] receiving object light, converting the object light intoluminance signals of a plurality of areas, calculating a histogram of aluminance distribution on the basis of the converted luminance signalsof the plurality of areas, and controlling operation of an illuminationdevice for illuminating an object based on a result of the calculating.

[0052] A flash photographing method according to the present inventionis characterized by being configured as follows.

[0053] The flash photographing method comprises:

[0054] receiving object light, converting the object light intoluminance signals of a plurality of areas, calculating a histogram of aluminance distribution on the basis of the converted luminance signalsof the plurality of areas, and controlling flash photographing operationbased on a result of the calculating.

[0055] A computer program product of the present invention, according toits first aspect, is characterized by being configured as follows.

[0056] The computer program product for supplying a control program foran illumination device comprises:

[0057] receiving object light, converting the object light intoluminance signals of a plurality of areas, calculating a histogram of aluminance distribution on the basis of the converted luminance signalsof the plurality of areas, and controlling operation of an illuminationdevice for illuminating an object based on a result of the calculating.

[0058] A computer program product of the present invention, according toits second aspect, is characterized by being configured as follows:

[0059] The computer program product for supplying a flash photographingcontrol program comprises:

[0060] receiving object light, converting the object light intoluminance signals of a plurality of areas, calculating a histogram of aluminance distribution on the basis of the converted luminance signalsof the plurality of areas, and controlling flash photographing operationbased on a result of the calculating.

[0061] Other objects and advantages besides those discussed above shallbe apparent to those skilled in the art from the description of apreferred embodiment of the invention which follows. In the description,reference is made to accompanying drawings, which form a part thereof,and which illustrate an example of the invention. Such example, however,is not exhaustive of the various embodiments of the invention, andtherefore reference is made to the claims which follow the descriptionfor determining the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062]FIG. 1 is a block diagram showing an image sensing apparatusaccording to the first embodiment of the present invention;

[0063]FIG. 2 is a block diagram showing a conventional image sensingapparatus;

[0064]FIG. 3 is a flow chart for explaining the operation of theconventional image sensing apparatus;

[0065]FIG. 4 is a view for explaining photographing conditions for anobject;

[0066]FIGS. 5a to 5 d are views for explaining the photographing statesof objects;

[0067]FIGS. 6a and 6 b are block diagrams showing how block segmentationand detection are performed in the first embodiment;

[0068]FIGS. 7A and 7B are graphs showing how histograms are calculatedin the first embodiment;

[0069]FIG. 8 is a flow chart for explaining the operation of an imagesensing apparatus according to the first embodiment;

[0070]FIG. 9 is a block diagram showing an image sensing apparatusaccording to the second embodiment;

[0071]FIG. 10A is a flow chart for explaining the operation of the imagesensing apparatus according to the second embodiment;

[0072]FIG. 10B is a flow chart for explaining the operation of the imagesensing apparatus according to the second embodiment;

[0073]FIG. 11 is a block diagram showing an image sensing apparatusaccording to the third embodiment;

[0074]FIGS. 12A and 12B are views showing how a frame is segmented;

[0075]FIG. 13A is a flow chart for explaining the operation of the imagesensing apparatus according to the third embodiment;

[0076]FIG. 13B is a flow chart for explaining the operation of the imagesensing apparatus according to the third embodiment;

[0077]FIG. 14 is a block diagram showing an image sensing apparatusaccording to the fourth embodiment;

[0078]FIG. 15A is a flow chart for explaining the operation of the imagesensing apparatus according to the fourth embodiment; and

[0079]FIG. 15B is a flow chart for explaining the operation of the imagesensing apparatus according to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] The preferred embodiments of the present invention will bedescribed in detail below with reference to the accompanying drawings.

[0081] (First Embodiment)

[0082]FIG. 1 is a block diagram showing the arrangement of an imagesensing apparatus according to the first embodiment of the presentinvention.

[0083] The same reference numerals as in FIG. 2 denote the same parts inFIG. 1, and a detailed description thereof will be omitted.

[0084] The arrangement of this embodiment differs from that of the priorart described above in that a block segmentation means 31, histogramgenerating means 41, and luminance distribution determination means 42are added.

[0085] An object image formed on the imaging plane of an image sensingelement 161 through imaging optical systems 150 and 152 and stop 151 isphotoelectrically converted. The resultant signal is processed by acamera signal processing circuit 162. Of the video signal, the luminancesignal is segmented into unit frames by the block segmentation means 31.This block segmentation is performed to divide the luminance signal intounit frames formed by a plurality of partitioned areas as shown in FIG.6a.

[0086] A detection means 1 performs detection processing, e.g., integralprocessing, for each unit frame of the segmented luminance signal. Thehistogram generating means 41 then generates a histogram in accordancewith the luminance levels obtained in units of blocks. The luminancedistribution determination means 42 determines this histogramdistribution and, more specifically, the magnitudes of histogram levelsexhibiting low luminance levels.

[0087] In a photographing condition in which the distribution of lowluminance levels is large, the background may occupy a large portion ofthe overall imaging angle of view and be located at a long distance. Inother words, the main object occupies a small portion of the overallframe, and hence the proportion of blocks to which importance must beattached in determining an exposure is small.

[0088] If the proportion of low-luminance portions is high as in theabove case, the luminance distribution determination means 42invalidates this low luminance level information and obtains the sumtotal of the luminance levels of the remaining blocks as a detectionsignal for determining an exposure. A comparator 36 on the next stagethen compares the sum total of luminance levels with a reference value35 to determine the validity of the above amount of light emitted.

[0089] A flash control means 4 determines the amount of light emitted onthe basis of input detection data as in the prior art, and controls theemission of a flash unit 5 in the determined amount of light emitted.For example, the flash control means 4 determines the amount of lightemitted by determining a proper exposure, overexposure, or underexposureon the basis of the sum total of input detection data.

[0090] Histogram processing of the above luminance distribution will bedescribed with reference to FIGS. 6a and 6 b.

[0091] The frame denoted by reference numeral 25 in FIG. 6a is anoverall sensed image. Reference numeral 6 denotes a main object. FIG. 6bshows how the portion in a circle 28 is enlarged, and a luminancehistogram is formed. The rectangular blocks shown in FIG. 6b are formedsuch that the segmented frames are detected to assign a plurality ofluminance levels to the respective frames, and numbers corresponding tothe luminance levels are assigned to the respective frames. In thiscase, 11 luminance levels, from 0 to 10, are determined, and therespective frames are numbered accordingly. The number of blocks thatcan take the same value is counted in units of numbers representing theluminance levels in the overall frame, thus forming a histogram of aluminance distribution. FIG. 7A shows such a histogram. FIG. 7A showsthe histogram of the luminance distribution under the object conditionshown in FIGS. 6a and 6 b. This histogram shows an extremely unevendistribution in which the number of blocks numbered “0” is the largest,and the number of blocks numbered “10” is the next largest. The numberof blocks numbered “0” representing the lowest luminance is largebecause a distant background that auxiliary light cannot reach when itis emitted occupies a high proportion of the overall frame. In addition,the number of blocks numbered “10” representing the highest luminance islarge because an object at a short distance, where the auxiliary lightcan easily reach, exists in the same frame.

[0092] In this case, the value “0” greatly deviates from a properexposure on the dark side, whereas the value “10” greatly deviates fromthe proper exposure on the bright side. Assume that the luminanceaverage of the overall frame is obtained as in the prior art. In thiscase, an exposure is determined from this average value, and a properexposure or slight underexposure is determined. Considering exposurecontrol for setting a proper exposure for the main object, anoverexposure is set for the main object by the conventional technique.

[0093] This is obvious from the fact that the average value of aluminance histogram distribution under an ideal object illuminationcondition like that shown in FIG. 7B is almost equal to that of theluminance histogram distribution shown in FIG. 7A described above.

[0094] In this embodiment, therefore, if it is determined on the basisof a histogram distribution that the proportion of low-luminanceportions to the overall frame is high, an exposure level is calculatedwithout adding the low-luminance-level components, thereby preparing formain emission to be performed next. An exposure state is thereforecalculated, excluding the above low luminance level. That is, anexposure amount is calculated by using exposure levels excluding adistant object where auxiliary light cannot reach, thereby allowingexposure control with importance being attached to the main object.

[0095] The above operation will be described with reference to the flowchart of FIG. 8.

[0096] The steps in this flow chart will be sequentially describedbelow.

[0097] Step S71: This step is the beginning of the flow, which starts insynchronism with, for example, the operation of an imaging start switch.

[0098] Step S72: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0099] Step S73: At the same time the flash unit 5 auxiliary emitslight, a sensed image is converted into an electrical image signal.

[0100] Step S74: The sensed image signal is segmented into blocks.

[0101] Step S75: A detection signal is generated from each sensed signalsegmented as a block which is a unit frame.

[0102] Step S76: A histogram is generated from the detection dataobtained in units of blocks.

[0103] Step S77: A histogram pattern is determined.

[0104] More specifically, it is checked on the basis of the proportionof low-luminance-level blocks whether the proportion of a distant objectto the imaging frame exceeds a predetermined reference value (pattern A)or not (pattern B).

[0105] Step S78: If the low-luminance-level histogram components exceeda predetermined amount, the amount of light emitted from the flash unit5 is determined, excluding the low-luminance-level blocks (e.g., theblocks numbered “0”).

[0106] Step S79: If the low-luminance-level histogram components areequal to or less than the predetermined amount, the amount of lightemitted from the flash unit 5 is determined, including all the blocks.

[0107] Step S80: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0108] Step S81: At the same time the flash unit 5 emits light, a sensedimage is converted into an image signal.

[0109] Step S82: This flow is terminated.

[0110] With this above operation, in photographing operation with theemission of auxiliary light, a proper exposure can be achievedregardless of the positions of objects, the brightness of thebackground, the proportion of the main object, and the like.

[0111] Note that a frame may be segmented into blocks in minimum orlarger pixel units of the image sensing elements. In general, as theframe is segmented in smaller units, control can be performed withhigher precision. In addition, for the sake of descriptive convenience,a histogram is formed on the basis of 11 levels, from 0 to 10. However,the number of levels can also be increased.

[0112] (Second Embodiment)

[0113]FIG. 9 is a block diagram showing the arrangement of an imagesensing apparatus according to the second embodiment of the presentinvention.

[0114] The same reference numerals as in the prior art and the firstembodiment denote the same parts in FIG. 9, and a detailed descriptionthereof will be omitted.

[0115] The first embodiment is based on a so-called TTL exposure controlscheme in which a common optical system is used for the imaging lens andexposure control. In the second embodiment, however, a scheme usingdifferent optical systems for an imaging optical system and exposurecontrol will be described.

[0116] Referring to FIG. 9, reference numerals 150 and 152 denoteimaging optical systems dedicated to image sensing operation and serveto form an object image on an imaging plane.

[0117] Reference numeral 151 denotes a stop interposed between theimaging optical systems 150 and 152. This stop is generally disposed inan afocal (parallel light) range.

[0118] Reference numeral 262 denotes a photoelectric conversion elementfor converting the amount of light imaged into an electrical (or charge)quantity, or an element whose physical properties are changed by light,e.g., a silver halide film containing a sensitizer.

[0119] Reference numeral 264 denotes a shutter curtain having amechanism of opening/closing for a predetermined period of time inimaging operation. Although not shown, assume that an opening/closingmechanism for the shutter curtain 264 is also provided, which operatesin synchronism with the operation of the shutter button.

[0120] Reference numeral 263 denotes a stop encoder for detecting andoutputting the current aperture value.

[0121] In this embodiment, as in the first embodiment, a blocksegmentation means 31 segments the luminance signal of a video signalinto unit frames, a detection means 1 performs detection processing suchas integral processing, and a histogram generating means 41 generates ahistogram in accordance with the luminance levels obtained in units ofunit blocks. A luminance distribution determination means 42 determinesthe magnitude of histogram levels as low luminance levels in thishistogram distribution, and obtains a detection signal by using only thedata of luminance blocks determined as valid blocks. A comparator 36compares the sum total of luminance levels with a reference value 35 todetermine the excess/shortage of the amount of light emitted.

[0122] A characteristic feature of the second embodiment is that a flashcontrol means 4 determines the amount of light emitted on the basis ofthe amount by which the stop 151 disposed in the imaging optical systemis stopped down, as well as the excess/shortage of the amount of lightemitted, and a flash unit 5 emits light in the obtained amount.

[0123] These operations will be described with reference to FIGS. 10Aand 10B.

[0124] The steps in the flow charts will be sequentially describedbelow.

[0125] Step S101: This step is the beginning of the flow, which startsin synchronism with, for example, the operation of an imaging startswitch.

[0126] Step S102: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0127] Step S103: At the same time auxiliary emission of the flash unit5 is performed, a sensed image is converted into an electrical imagesignal.

[0128] Step S104: The sensed image signal is captured, and the image issegmented into blocks.

[0129] Step S105: A detection signal is generated from each sensedsignal segmented as a block.

[0130] Step S106: A histogram is generated from the detection dataobtained in units of blocks.

[0131] Step S107: A histogram pattern is determined.

[0132] More specifically, it is checked on the basis of the proportionof low-luminance-level blocks whether the proportion of a distant objectto the imaging frame exceeds a predetermined reference value (pattern A)or not (pattern B).

[0133] Step S108: If the low-luminance-level histogram components exceeda predetermined amount, the amount of light emitted from the flash unit5 is determined, excluding the low-luminance-level blocks (e.g., theblocks numbered “0”).

[0134] Step S109: If the low-luminance-level histogram components areequal to or less than the predetermined amount, the amount of lightemitted from the flash unit 5 is determined, including all the blocks.

[0135] In step S110: An exposure level is determined from thetemporarily determined amount of light emitted and stop information, andthe amount of light emitted from the flash unit 5 is finally determined.

[0136] In this case, the stop information is used to determine a properexposure, overexposure, or underexposure with respect to the amount ofobject light passing through an optical system 250 without any stop inconsideration of the amount of light passing through the imaging opticalsystems 150 and 152 including the stop 151.

[0137] In general, as the stop is stopped down in one level, the amountof light emitted is doubled.

[0138] Step S114: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0139] step S115: The shutter curtain 264 is opened to guide light tothe photoelectric conversion element, silver halide film, or the like.

[0140] Step S116: At the same time the flash unit 5 emits light, asensed image is converted into an image signal.

[0141] Step S117: The shutter curtain 264 is closed.

[0142] Step S118: This flow is terminated.

[0143] With the above operation, photographing with the emission ofauxiliary light can be performed with a proper exposure.

[0144] The same condition as in FIG. 6 suffices for the segmentation ofthe sensed image. Only the blocks that are greatly influenced by changesin luminance upon emission of auxiliary light are used for actualexposure control.

[0145] In this description, the luminance levels of sensed signals areused for a histogram. However, for example, histograms may be generatedfrom the signal levels of signals of three colors, i.e., red, blue, andgreen signals, obtained by color-separating a sensed signal, and therespective signal levels may be processed on the basis of the sameprinciple as that of the luminance distribution determination means 42.Thereafter, the detection average of the signals of the three colors maybe calculated to perform flash control.

[0146] (Third Embodiment)

[0147]FIG. 11 is a block diagram showing the arrangement of an imagesensing apparatus according to the third embodiment of the presentinvention.

[0148] The same reference numerals as in the prior art shown in FIG. 2denote the same parts in FIG. 11, and a detailed description thereofwill be omitted.

[0149] The arrangement of this embodiment differs from that of the priorart in that a block segmentation means 331, storage means 332, andpassing/blocking means 333 are added.

[0150] The following processing is performed before a flash unit 5 iscaused to emit light. An object image formed on the imaging plane of animage sensing element 161 through an imaging optical systems 150 and 152and stop 151 is photoelectrically converted. The resultant signal issubjected to signal processing in a camera signal processing circuit162. The block segmentation means 331 segments the luminance signal ofthe video signal into unit frames. A detection means 1 performsdetection processing such as integral processing for the respective unitframes of the segmented luminance signals. The detection signals outputfrom the detection means 1 are stored in the storage means 332 in unitsof blocks. This block segmentation is performed such that the frame issegmented into unit frames formed by, for example, 8×6 areas.

[0151] The following processing is performed after an image is capturedat the same time the flash unit 5 emits light. The luminance signalcomponent of the sensed image obtained upon preliminary emission of theflash unit 5 is input to the block segmentation means 331 to besegmented into unit frames as in the above case. The detection means 1performs detection processing, e.g., integral processing described inthe prior art, for the respective unit frames.

[0152] A subtraction circuit 334 performs subtraction processing for thedetection value in each block as each unit frame at the time ofpreliminary emission of auxiliary light and the detection value in acorresponding block without emission of auxiliary light. A comparator336 then compares the calculation result with a predetermined referencevalue 335.

[0153] If the difference output based on a given block as a unit frametakes a value larger than the reference value 335, it is determined thatthe detection data of the block is valid, and the data is input to aflash control means 4 through the passing/blocking means 333. Incontrast to this, if the output takes a value smaller than the referencevalue 335, it is determined that the detection data of the block isinvalid, and the data is blocked by the passing/blocking means 333 andis not input to the flash control means 4.

[0154] The flash control means 4 determines the amount of light emittedon the basis of the input detection data and controls the emission ofthe flash unit 5 in the determined amount as in the prior art. Forexample, the flash control means 4 determines the amount of lightemitted by determining a proper exposure, overexposure, or underexposureon the basis of the sum total of the input detection data.

[0155] The above operation will be described with reference to the flowcharts of FIGS. 13A and 13B.

[0156] The steps in the flow charts will be sequentially describedbelow.

[0157] Step S371: This step is the beginning of the flow, which startsin synchronism with, for example, the operation of an imaging startswitch.

[0158] Step S372: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0159] Step S373: A sensed image is captured and converted into an imagesignal (without emission of the flash unit).

[0160] Step S374: The sensed image signal is segmented into blocks.

[0161] Step S375: A detection signal is generated from each sensed imagesegmented as a block which is a unit frame.

[0162] Step S376: The detection data in the respective blocks are storedin the storage means.

[0163] Step S377: Preliminary emission of the flash unit is performed.

[0164] Step S378: A sensed image is captured and converted into an imagesignal.

[0165] Step S379: The sensed image is segmented into blocks as unitframes.

[0166] Step S380: A detection signal is generated from each sensedsignal segmented as a block.

[0167] Step S381: The detection data stored in the storage means 332 issubtracted from each detection signal in units of blocks, and eachresult is compared with the reference value 335.

[0168] If the comparison result indicates calculation result >referencevalue, the flow advances to step S382. If the comparison resultindicates calculation result≦reference value, the flow advances to stepS383.

[0169] Step S382: It is determined that the data of the detected blockis valid, and the data is passed through the passing/blocking means 333.

[0170] Step S383: It is determined that the data of detected block isinvalid, and the data is blocked by the passing/blocking means 333.

[0171] Step S384: An exposure level is determined from the detectionsignal.

[0172] If a proper exposure is determined, the flow advances to stepS385. If an underexposure is determined, the flow advances to step S386.If an overexposure is determined, the flow advances to step S387.

[0173] Step S385: Preparation for emission is done with the same lightamount as in preliminary emission, and the flow advances to step S388.

[0174] Step S386: Preparation for emission is done by increasing theamount of light emitted by the shortage in preliminary emission, and theflow advances to step S388.

[0175] Step S387: Preparation for emission is done by decreasing theamount of light emitted by the excess in preliminary emission, and theflow advances to step S388.

[0176] Step S388: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0177] Step S389: At the same time the flash unit 5 emits light, asensed image is converted into an image signal.

[0178] Step S390: This flow is terminated.

[0179] With the above operation, in photographing operation with theemission of auxiliary light, a proper exposure can be achievedregardless of the positions of objects, the brightness of thebackground, the proportion of the main object, and the like.

[0180] The segmentation of the sensed image in the above operation willbe described next with reference to FIGS. 12A and 12B.

[0181]FIG. 12A shows a specific area of a sensed image which is selectedunder the same condition as that described with reference to FIGS. 5a to5 d. Referring to FIG. 12A, the 8×9 squares indicate blocks segmented asunit frames.

[0182] Only the blocks in a selection frame 429 indicated by the thickline are used as information for exposure control. Likewise, in the caseshown in FIG. 12B, only the blocks in a selection frame 429′ are used asinformation for exposure control.

[0183] In this range, the object is located closer to the photographerthan the background, and hence flash light as auxiliary light can easilyreach the object. As described in the above flow, the detection value ofeach unit frame stored in the storage means 332 is subtracted from thedetection signal of a corresponding unit frame in units of blocks, andthe subtraction result is compared with the reference value 335. As aconsequence, only the blocks in which values indicating the degrees ofinfluence on changes in luminance upon emission of auxiliary light arelarge (i.e., only the blocks in which the main object exists) are usedfor actual exposure control. This makes it possible to obtain a properexposure regardless of the proportion of the main object at the shortdistance to the sensed image.

[0184] (Fourth Embodiment)

[0185]FIG. 14 is a block diagram showing the arrangement of an imagesensing apparatus according to the fourth embodiment of the presentinvention.

[0186] The same reference numerals as in the prior art and thirdembodiment denote the same parts in FIG. 14, and a detailed descriptionthereof will be omitted.

[0187] The third embodiment is based on the so-called TTL exposurecontrol scheme in which a common optical system is used for the imaginglens and exposure control. In the fourth embodiment, however, a schemeusing different optical systems for an imaging optical system andexposure control will be described.

[0188] Referring to FIG. 14, reference numerals 150 and 152 denoteimaging optical systems dedicated to imaging operation, and serve toform an object image on the imaging plane.

[0189] Reference numeral 151 denotes a stop interposed between theimaging optical systems 150 and 152. This stop is generally disposed inan afocal (parallel light) range.

[0190] Reference numeral 462 denotes a photoelectric conversion elementfor converting the amount of light imaged into a quantity of electricity(or charge), or an element whose physical properties are changed bylight, e.g., a silver halide film containing a sensitizer.

[0191] Reference numeral 464 denotes a shutter curtain having amechanism of opening/closing for a predetermined period of time inimaging operation. Although not shown, assume that an opening/closingmechanism for the shutter curtain 464 is also provided, which operatesin synchronism with the operation of the shutter button.

[0192] Reference numeral 463 denotes a stop encoder for detecting andoutputting the current aperture value.

[0193] In this embodiment, as in the third embodiment, the followingprocessing is performed before a flash unit 5 is caused to emit light. Asignal processing circuit 262 performs signal processing for theelectrical signal obtained by an image sensing element 461 byphotoelectric conversion. A block segmentation means 331 breaks up theluminance component into unit frames. A detection means 1 performsdetection processing such as integral processing for the respectivesegmented unit frames. The detection signals output from the detectionmeans are stored in a storage means 332 in units of blocks.

[0194] Note that in this embodiment, the number of photoelectricconversion elements in the image sensing element 461 may be equal to theminimum number of blocks. For example, with the segmentation shown inFIG. 12, at least photoelectric conversion elements corresponding to 8×9blocks will suffice.

[0195] The following processing is performed after the image is capturedat the timing of emission of the flash unit 5. The luminance componentof the sensed image obtained at the time of emission of the flash unit 5is input to the block segmentation means 331 to be segmented into unitframes. The detection means 1 performs detection processing such asintegral processing for the respective segmented unit frames.

[0196] A subtraction circuit 334 performs subtraction processing for thedetection value of each block upon emission of auxiliary light and thedetection value of a corresponding block without emission of auxiliarylight. A comparator 336 then compares this calculation result with apredetermined reference value 335.

[0197] If the subtraction output takes a value larger than thepredetermined reference value 335, it is determined that the detectiondata of the block is valid, and the data is input to a flash controlmeans 4 through a passing/blocking means 333. In contrast to this, ifthe subtraction output takes a value smaller than the reference value335, it is determined that the detection data of the block is invalid,and the data is blocked by the passing/blocking means 333 and is notinput to the flash control means 4.

[0198] The flash control means 4 determines the amount of light emittedon the basis of the input detection data and the amount by which thestop 151 disposed in the imaging optical system is stopped down, andcauses the flash unit 5 to emit light in the determined amount.

[0199] These operations will be described with reference to the flowcharts of FIGS. 15A and 15B.

[0200] The steps in the flow charts will be sequentially describedbelow.

[0201] Step S471: This step is the beginning of the flow, which startsin synchronism with, for example, the operation of an imaging startswitch.

[0202] Step S472: It is checked whether the flash unit 5 is completelycharged. If the flash unit is not completely charged, the flow waitsuntil charging is completed.

[0203] Step S473: A sensed image is captured and converted into an imagesignal (without emission of the flash unit).

[0204] Step S474: The sensed image signal is segmented into blocks.

[0205] Step S475: A detection signal is generated from each sensedsignal segmented as a block.

[0206] Step S476: The detection data of each block is stored in thestorage means 332.

[0207] Step S477: Preliminary emission of the flash unit is performed.

[0208] Step S478: The sensed image is captured and converted into animage signal.

[0209] Step S479: The sensed image is segmented into unit frames asblocks.

[0210] Step S480: A detection signal is generated from each sensedsignal segmented as a block.

[0211] Step S481: The detection data stored in the storage means 332 issubtracted from detection signal, and the result is compared with thereference value 335.

[0212] If the comparison result indicates calculation result >referencevalue, the flow advances to step S482. If the comparison resultindicates calculation result≦reference value, the flow advances to stepS483.

[0213] Step S482: It is determined that the detected block data isvalid, and the data is passed through the passing/blocking means 333.

[0214] Step S483: It is determined that the detected block data isinvalid, and the data is blocked by the passing/blocking means 333.

[0215] Step S484: An exposure level is checked from the detection signaland stop information.

[0216] If the exposure is proper, the flow advances to step S485. If anunderexposure is determined, the flow advances to step S486. If anoverexposure is determined, the flow advances to step S487.

[0217] In this case, the stop information is used to determine a properexposure, overexposure, or underexposure with respect to the amountof-object light passing through an optical system 450 without any stopin consideration of the amount of light passing through the imagingoptical systems 150 and 152 including the stop 151.

[0218] Step S485: Preparation for emission is done in the same lightamount as that in the preceding emission, and the flow advances to stepS488.

[0219] Step S486: Preparation for emission is done by increasing theamount of light emitted in accordance with the preceding underexposure.The flow then advances to step S488.

[0220] Step S487: Preparation for emission is done by decreasing theamount of light emitted in accordance with the preceding overexposure.The flow then advances to step S488.

[0221] Step S488: It is checked whether the flash unit 5 is completelycharted. If the flash unit 5 is not completely charged, the flow waitsuntil changing is completed.

[0222] Step S489: The shutter curtain 464 is opened to guide light tothe photoelectric conversion element, silver halide film, or the like.

[0223] Step S490: At the same time the flash unit 5 emits light, asensed image is converted into and image signal.

[0224] Step S491: The shutter curtain 464 is closed.

[0225] Step S492: This flow is terminated.

[0226] With the above operations, proper exposure can be performed inphotographing operation with emission of auxiliary light. The samecondition as in FIG. 12 suffices for the segmentation of the sensedimage. Only the blocks that are greatly influenced by changes inluminance upon emission of auxiliary light are used for actual exposurecontrol.

[0227] [Other Embodiments]

[0228] The present invention can be applied to a system constituted by aplurality of devices (e.g., host computer, interface, reader, printer)or to an apparatus comprising a signal device (e.g., copying machine,facsimile machine).

[0229] Further, the object of the present invention can also be achievedby providing a storage medium (or recording medium) storing programcodes for implementing the aforesaid function of the above embodimentsto a system or apparatus, reading the program codes, by a computer(CPUor MPU) of the system or apparatus, from the storage medium, thenexecuting the program. In this case, the program codes read from thestorage medium realize the functions according to the embodiments, andstorage medium storing the program codes constitutes the invention.Furthermore, besides aforesaid functions according to the aboveembodiment are realized by executing the program codes which are read bya computer, the present invention includes a case where an OS (operatingsystem) or the like running on the computer performs a part or entireprocesses in accordance with designations of the program codes andrealizes functions according to the above embodiments.

[0230] Furthermore, the present invention also includes a case where,after the program codes read form the storage medium are written in afunction expansion card which is inserted into the computer or in amemory provided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program codes and realizes functions of the above embodiments.

[0231] When the present invention is to be applied to the above storagemedium, program codes corresponding to the flow charts described above(shown in FIGS. 8, 10, 13, and 15) are stored in the storage medium.

[0232] As has been described above, according to the first and secondembodiments, a sensed image obtained upon preliminary emission ofauxiliary light is segmented into a plurality of blocks and detected. Ahistogram corresponding to the detection levels of the respective blocksis calculated, and valid detection blocks for flash control on auxiliarylight are extracted on the basis of the histogram pattern of luminancelevels, thereby adjusting the amount of light emitted in main emission.

[0233] A proper exposure can be attained regardless of the proportion ofan object to the overall frame, the distance to the object, and thelike.

[0234] According to the third and fourth embodiments, a sensed image issegmented into a plurality of blocks, and it is checked, on the basis ofchange levels of object luminances in each block at the time of emissionof auxiliary light and at the time of no emission, whether the luminanceinformation of each segmented block is used for exposure control,thereby performing exposure control. With this operation, a properexposure can be achieved regardless of the proportion of an object tothe overall frame, the distance to the object, and the like.

[0235] In each embodiment described above, the amount of light emittedfrom the flash unit (including the emission time) is controlled inaccordance with luminance levels selected in accordance with thehistogram of luminance levels. However, in addition to the amount oflight emitted from the flash unit, other flash exposure factors such asthe stop and shutter may be controlled.

[0236] In each embodiment described above, a predetermined low luminancelevel is excluded in accordance with the histogram of luminance levels.In addition, a predetermined high luminance level may be excluded asneeded.

[0237] According to the present invention, flash photographing operationmay be controlled by assigning different weights to the respectiveluminance levels instead of completely excluding a predeterminedluminance level in accordance with the histogram of luminance levels.

[0238] In addition, according to the present invention, flashphotographing operation may be controlled on the basis of a histogramfrom which a predetermined luminance level is excluded from the verybeginning.

[0239] The software arrangements and hardware arrangements in theembodiments described above can be replaced, as needed.

[0240] In addition, the respective embodiments of the present inventionor their technical elements may be combined with each other, as needed.

[0241] In the present invention, all or some of the constituent elementsof each claim or embodiment may constitute one apparatus, combined withanother apparatus, or become elements of an apparatus.

[0242] The present invention can be applied to various types of camerassuch as electronic cameras for sensing moving images or still images,cameras using silver halide films, single-lens reflex cameras, lensshutter cameras, and monitoring cameras, other apparatuses such as imagesensing apparatuses other than cameras, image readers, and opticalapparatuses, apparatuses applied to the cameras, image sensingapparatuses, image readers, optical apparatuses, and other apparatuses,elements constituting these apparatuses, control methods for theapparatuses, and computer program products such as storage media forproviding the control methods.

[0243] As has been described above, according to each embodimentdescribed above, a main object can be properly exposed regardless of thecondition of the background.

[0244] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An apparatus comprising: (A) a photometric unitfor receiving object light and converting the object light intoluminance signals of a plurality of areas; and (B) a control unit forcalculating a histogram of a luminance distribution on the basis of theluminance signals of the plurality of areas converted by saidphotometric unit, said control unit controlling operation of anillumination device for illuminating an object based on a result of thecalculating.
 2. The apparatus according to claim 1 , wherein saidphotometric unit includes an image sensing element for converting objectlight into a video signal for photographing operation.
 3. The apparatusaccording to claim 1 , wherein said control unit controls the operationof the illumination device on the basis of a pattern of the calculatedhistogram.
 4. The apparatus according to claim 1 , wherein said controlunit controls the operation of the illumination device on the basis ofthe luminance signals which are used differently in accordance with apattern of the calculated histogram.
 5. The apparatus according to claim1 , wherein said control unit controls the operation of the illuminationdevice on the basis of luminance signals selected from the luminancesignals in accordance with a pattern of the calculated histogram.
 6. Theapparatus according claim 1 , wherein when a pattern of the calculatedhistogram indicates that luminance signals concentrate on apredetermined luminance level to not less than a predetermined degree,said control unit controls the operation of the illumination device onthe basis of luminance signals obtained by excluding the luminancesignals of the predetermined luminance levels from the luminancesignals.
 7. The apparatus according to claim 1 , wherein said controlunit controls an amount of light emitted from the illumination devicebased on a result of the calculating.
 8. The apparatus according toclaim 1 , wherein said control unit calculates the histogram on thebasis of a photometry result obtained by said photometric unit uponpreliminary illumination on the object.
 9. The apparatus according toclaim 8 , wherein said control unit controls the operation of theillumination device based on a result of the calculating whenphotography is performed.
 10. The apparatus according to claim 1 ,wherein said apparatus includes an image sensing apparatus.
 11. Theapparatus according to claim 1 , wherein said apparatus includes acamera.
 12. An apparatus comprising: (A) a photometric unit forreceiving object light and converting the object light into luminancesignals of a plurality of areas; and (B) a control unit for calculatinga histogram of a luminance distribution on the basis of the luminancesignals of the plurality of areas converted by said photometric unit,said control unit controlling flash photographing operation based on aresult of the calculating.
 13. The apparatus according to claim 12 ,wherein said photometric unit includes an image sensing element forconverting object light into a video signal for photographing operation.14. The apparatus according to claim 12 , wherein said control unitcontrols the flash photographing operation on the basis of a pattern ofthe calculated histogram.
 15. The apparatus according to claim 12 ,wherein said control unit controls the flash photographing operation onthe basis of the luminance signals which are used differently inaccordance with a pattern of the calculated histogram.
 16. The apparatusaccording to claim 12 , wherein said control unit controls the flashphotographing operation on the basis of luminance signals selected fromthe luminance signals in accordance with a pattern of the calculatedhistogram.
 17. The apparatus according claim 12 , wherein when a patternof the calculated histogram indicates that luminance signals concentrateon a predetermined luminance level to not less than a predetermineddegree, said control unit controls the flash photographing operation onthe basis of luminance signals obtained by excluding the luminancesignals of the predetermined luminance levels from the luminancesignals.
 18. The apparatus according to claim 12 , wherein said controlunit calculates the histogram on the basis of a photometry resultobtained by said photometric unit upon preliminary illumination on theobject.
 19. The apparatus according to claim 12 , wherein said apparatusincludes an image sensing apparatus.
 20. The apparatus according toclaim 12 , wherein said apparatus includes a camera.
 21. An illuminationdevice control method comprising: receiving object light, converting theobject light into luminance signals of a plurality of areas, calculatinga histogram of a luminance distribution on the basis of the convertedluminance signals of the plurality of areas, and controlling operationof an illumination device for illuminating an object based on a resultof the calculating.
 22. A flash photographing method comprising:receiving object light, converting the object light into luminancesignals of a plurality of areas, calculating a histogram of a luminancedistribution on the basis of the converted luminance signals of theplurality of areas, and controlling flash photographing operation basedon a result of the calculating.
 23. A computer program product forsupplying a control program for an illumination device, comprisingreceiving object light, converting the object light into luminancesignals of a plurality of areas, calculating a histogram of a luminancedistribution on the basis of the converted luminance signals of theplurality of areas, and controlling operation of an illumination devicefor illuminating an object based on a result of the calculating.
 24. Theproduct according to claim 23 , wherein said computer program productincludes a storage medium.
 25. A computer program product for supplyinga flash photographing control program, comprising receiving objectlight, converting the object light into luminance signals of a pluralityof areas, calculating a histogram of a luminance distribution on thebasis of the converted luminance signals of the plurality of areas, andcontrolling flash photographing operation based on a result of thecalculating.
 26. The product according to claim 25 , wherein saidcomputer program product includes a storage medium.